1. Technical Field
The present invention relates to a four-point seat belt device installed in a vehicle such as an automobile or the like.
2. Related Art
Seat belts for securing safety of a passenger are attached to a vehicle such as an automobile or the like. There are in use four-point seat belts having shoulder belts for pressing both shoulders of a passenger, other than three-point seat belts. Technology has been disclosed in Japanese Unexamined Patent Application Publication (JP-A) No. 2004-330975 which aims to improve restraint performance in a four-point seat belt device. To this end, wind-up force of a lap belt for pressing the waist is set so as to be greater than wind-up force of a shoulder belt for pressing the shoulder.
Technology has been disclosed in JP-A No. 2010-58679 wherein the payout lengths of the lap belts and the payout lengths of the shoulder belts are detected in order to appropriately set wearing positions for lap belts and wearing positions for shoulder belts. Adjustment control is then performed based on the detected payout lengths so as to reduce difference between the payout lengths of the left and right lap belts, and difference between the payout lengths of the left and right shoulder belts.
However, employing the above-described four-point seat belt device does not always restrain a passenger in an appropriate manner. For example, in the case of a passenger having a protruding abdomen, the lap belt may ride up on the upper side of the abdomen in the case of rapid deceleration which incurs restriction by the belt. Wearing the lap belt in such a state may cause the chest, which is higher than the abdomen, to be strongly restrained, while portions of the body lower than the chest are not restrained.
Also, it is desirable for the lap belt pressing the waist to press and restrain the hipbone of passengers having a body type of which the abdomen does not protrude so far that the belt rides up on the upper side of the abdomen. However, even if the lap belt moves to the lower side of the abdomen, the passenger is consequently not restrained if the belt is in a loosened state. Also, the passenger may find troublesome having to perform the motion of forcibly extracting the lap belt by hand, and moving this to the lower side of the abdomen.
Thus, if the seat belt is loose at the time of wearing, the body of the passenger is not restrained. On the other hand, automatically winding up the seat belt immediately after the passenger puts on the seat belt may restrain the passenger's chest as described above. Also, unlike three-point seat belts, four-point seat belt device is buckled in front of the passenger. Accordingly, the belt is loose immediately after being worn, and is not positioned at the waist of the passenger. Therefore, the passenger has to bring the lap belts to his/her waist. It is desirable for a lap belt pressing the waist to automatically restrain the waist so as to press the hipbone, without the passenger having to perform a bothersome action. This is true for passengers with a body type where the abdomen does not protrude so far that the belt rides up on the upper side of the abdomen.
Thus, there is demand for a four-point seat belt device which restrains the body without troubling the passenger, in accordance with various body types of passengers.